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The Pokérus (Japanese: ポケルス Pokérus), from "Pokémon virus", is a
microscopic life-form that may attach to Pokémon, first appearing in🧾 the Generation II
games. It is a beneficial mechanic that a Pokémon can obtain.
In the games
When a
Pokémon has the🧾 Pokérus, it gains double the effort values from battling (e.g.,
fighting a Magikarp will give two Speed EVs, rather than🧾 one). Effort points gained
from Vitamins and Feathers are not doubled. The infected Pokémon can infect other
Pokémon with the🧾 virus for a period of one to four days. However, the Pokérus timer can
be delayed by several methods, such🧾 as by placing the infected Pokémon in a PC
Box.
While it is represented similarly to status conditions, the Pokérus is🧾 not a
status condition, so it cannot be healed at a Pokémon Center or with any status
condition healing item.
Pokérus🧾 has a 3 in 65,536 (or approximately a 1 in 21,845)
chance of being generated on one of the player's🧾 Pokémon after a battle, making it
rarer than encountering or hatching a Shiny Pokémon. If any of the player's Pokémon🧾 are
infected, the Pokérus may spread among Pokémon in the player's party after any
battle.
From Generation IV onward, the Pokérus🧾 became more accessible, with worldwide
trading facilitated by Nintendo Wi-Fi Connection.
Infection
When a Pokémon is infected
with the Pokérus, their status🧾 screen will display an icon indicating this special
"status" the same way status conditions would be noted. If the Pokémon🧾 becomes affected
by a status condition such as Sleep, the Pokérus icon will be temporarily replaced
until the status condition🧾 is cured. As long as the Pokémon is infected with the
Pokérus, it can spread the virus to other Pokémon🧾 in the player's party.
The Pokérus
may spread if an infected Pokémon is in the player's party after a battle. The🧾 Pokérus
may only spread to a Pokémon directly adjacent to an already infected Pokémon, and only
if they have never🧾 had Pokérus before. Eggs may catch the Pokérus like any other
Pokémon.
Becoming cured
A Pokérus infection only progresses towards cured status🧾 when a
new day starts with the infected Pokémon in the party (or if, when the game is loaded,
it🧾 is not the same day as it was when the game was saved). The number of days before a
Pokémon🧾 will be cured of the Pokérus can vary from one to four days. Once this time has
passed, the Pokémon🧾 becomes cured and will be immune to the virus in the future. The
Pokémon still gains double effort values when🧾 cured.
Due to the beneficial nature of
the Pokérus, players will often place an infected Pokémon in the PC where it🧾 will keep
the infection indefinitely, so that it may be withdrawn to spread the virus at will.
Other options include🧾 putting a Pokémon in the Day Care or sending it to Stadium 2 in
Generation II, Pokémon Box Ruby &🧾 Sapphire in Generation III, My Pokémon Ranch in
Generation IV, Pokémon Bank in Generation VI and Generation VII, or Pokémon🧾 HOME in
Generation VIII.
In Generation III, if the player deposits an infected Pokémon inside a
PC, saves inside a Pokémon🧾 Center prior to midnight, shuts off the game, resumes the
game after midnight, withdraws the infected Pokémon from the PC,🧾 and exits the Pokémon
Center, it is possible for the infected Pokémon to be cured of the Pokérus upon
stepping🧾 outside of the building. This does not happen in any other generation.
In
Generation VIII, the game will check on the🧾 next available random event increment after
midnight. This can result in a Pokémon that was infected while in a box,🧾 and withdrawn
directly after resuming the game from sleep, being subsequently cured of the Pokérus
after the next battle or🧾 similar event.
Technical information
The Pokérus is stored in
a Pokémon's data structure as a single byte. In hexadecimal, this can be🧾 represented as
a two-digit number XY. The upper 4 bits of the byte, X, represent the specific strain
of the🧾 Pokérus the Pokémon has contracted. The lower 4 bits, Y, represent the number of
days remaining before the infected Pokémon🧾 is cured of the virus.
A Pokémon is or has
been infected if X (the strain) is a nonzero value. If🧾 Y (days remaining) is nonzero
when X is also nonzero, this means the Pokémon is currently infected. If Y is🧾 0 and X
is nonzero, then the Pokémon is "cured" of the Pokérus. If both X and Y are 0,🧾 then the
Pokémon has never been affected by the Pokérus.
Whenever the game's internal clock
strikes midnight, every currently infected Pokémon🧾 in the player's party has their
Pokérus value decreased by one. Once the Y value reaches 0, the Pokémon will🧾 be cured
of the Pokérus.
Strains
Whenever the game creates the Pokérus on a Pokémon, the value
assigned to Y (days) depends🧾 on the value assigned to X (strain). Specifically, the
number of days will be set to X modulo 4 +🧾 1. In other words, the higher two bits of X
are irrelevant to the "strain".
Strain X values Duration
(Y value) A🧾 0, 4, 8, 12 1 day
B 1, 5, 9, 13 2 days C 2, 6, 10, 14 3 days🧾 D 3, 7, 11, 15 4 days
Whenever the Pokérus
spreads from an infected Pokémon to a new Pokémon, the new🧾 Pokémon inherits the
infected Pokémon's strain of the Pokérus (X) and Y is copied directly from the infected
Pokémon. As🧾 an example, if a Pokémon has the Pokérus with an X value of 7 and a Y value
of 2🧾 (2 days remaining before it will be cured) and it infects another Pokémon, the new
Pokémon will be infected with🧾 Pokérus with an X value of 7 and a Y value of 2.
Infecting other Pokémon does not reset the🧾 Y value to the default value for a given
strain on the newly infected Pokémon, nor for the original host.
In🧾 Pokémon Emerald
onward, X values of 0 and 8 do not generate legitimately, as the RNG doesn't permit
these values🧾 to generate. Additionally with a value of 0, upon being "cured" the
Pokémon would appear to have never had the🧾 Pokérus at all.
After having the virus
Once
a Pokémon's immune system has fought off the virus, they cannot spread it further,🧾 nor
can it be spread to them by other Pokémon. In Generations II and III, a dot will appear
on🧾 the Pokémon's status screen to indicate that they have had the virus previously,
while in Generation IV and onward, it🧾 will be a small face. Though the virus is gone,
the Pokémon will still gain twice the EVs it would🧾 have gained before the
virus.
Differences between generations
Generation II
When the player first encounters
the virus in one of the Generation II🧾 games, the nurse at the Pokémon Center will make
note of it when the Pokémon is first healed after contracting🧾 it, saying that there are
"tiny life forms" on the Pokémon. After leaving the Pokémon Center, Professor Elm will
call🧾 the player to tell them that the virus has no effect and will wear off. A Pokémon
with active Pokérus🧾 will list its status as such, and a Pokémon that has had the
Pokérus and is cured will have a🧾 small dot near its HP meter on the status screen. At
the end of a battle, the virus has a🧾 1/3 chance to spread. If the infected Pokémon is
adjacent to two Pokémon who have never had it before, one🧾 of them will catch the
Pokérus. Pokérus can infect Eggs as well. An indicator for Pokérus will not show up🧾 on
the Egg's status screen, but once it hatches, it will appear under its status on the
status screen like🧾 normal.
If a Pokémon with any stage of the Pokérus (active or cured)
is traded back to a Generation I game,🧾 or withdrawn from Pokémon Stadium 2 by a
Generation I game, all traces of that Pokémon having had the Pokérus🧾 will disappear.
This is because a Pokémon's Pokérus status is not saved in any form in the Generation I
games,🧾 thereby making it possible for a Pokémon to legitimately contract the Pokérus
multiple times by trading it back and forth,🧾 once it becomes cured of a given
infection. The only benefit of doing so would be to allow other Pokémon🧾 to contract the
virus.
The Pokérus cannot randomly occur before the player has visited Goldenrod
City[1] (but it may spread between🧾 Pokémon before then). If a Pokémon in the party has
the Pokérus, other Pokémon cannot randomly contract it; they can🧾 only receive it from
that Pokémon.[2]
Infection and spread details
This section is incomplete.
Please feel
free to edit this section to add🧾 missing information and complete it.
Reason:
Description of the random byte generation algorithm, which is that used by other random
byte-needing🧾 routines
The party is first iterated over to determine if any member has
the Pokérus. If so, the spread code is🧾 called for each member with the Pokérus and not
the new infection code, and if not vice versa.
The spread code🧾 checks if a random byte
is less than 85 and if the party has multiple members before proceeding as follows:🧾 if
the spreader is the last party member, or if a random byte is less than 128, iterate
backwards, otherwise🧾 iterate forwards. If the member being iterated over has an active
infection, they are skipped over and become the spreader.🧾 If they are clear and never
had the Pokérus, they are infected. The Y value for an infection is generated🧾 from the
X value as it is for a spontaneous infection, unlike in future games where it is
copied. The🧾 iteration stops when a member is newly infected, when it reaches a cured
member, or when it would be about🧾 to pass through the beginning or end of the
party.
The new infection code first checks if the flag for having🧾 visited Goldenrod
City is set, terminating if not. Then, it checks if a random byte is equal to zero and
🧾 another random byte is less than three, terminating if not. It then chooses a random
party member by generating a🧾 random byte and keeping its bottom three bits (bitwise and
with seven), rerolling until that number is a valid party🧾 index. If that party member
has ever had the Pokérus, the code terminates. Otherwise, a random byte is rolled,
rerolling🧾 if zero until not zero. This byte shall be represented as AB (not to be
confused with registers A and🧾 B) in the same way that the Pokérus byte is represented
as XY. If A is not zero, B's bottom🧾 three bits (bitwise and with seven) are copied as a
four-bit value, incremented, and put into X, and X's bottom🧾 two bits (bitwise and with
three) are copied as a three-bit value, incremented, and put into Y. Otherwise, it is
🧾 likely intended to copy B into X, but, perhaps due to a misplaced load, zero is copied
into X instead;🧾 Y is then derived from X with the same code as with A not zero, but
since X is always🧾 zero, Y is always one. (If the misplaced load is placed in a more
logical place, the Y value ends🧾 up always being one anyway, so there may have been more
required effort to make the code work as intended.)
X🧾 values of zero and eight can
occur naturally: the latter is as designed, the former is due to the above🧾 bug. Due to
this bug, an X value above eight cannot occur naturally. Probabilities of each strain
is as follows:
X🧾 values Chance to occur 0 15/255
(5.88235%) 1, 2, 3, 4, 5, 6, 7, 8
30/255
(11.76471%) 9, 10, 11, 12, 13,🧾 14, 15 0/255
(Cannot naturally occur)
Generation
III
The Pokérus can only be contracted or cured in Ruby, Sapphire, and Emerald. In
FireRed🧾 and LeafGreen, as well as Colosseum and Pokémon XD, since the time function is
absent, a Pokémon with the Pokérus🧾 will keep it indefinitely (it can't spread the
Pokérus, either), until it is transferred to the Hoenn-based games. When a🧾 Pokémon can
spread the Pokérus, it has a 1/3 chance to spread it to both adjacent
Pokémon.
Otherwise, the Pokérus operates🧾 in much the same way as in Generation II, but
it is now possible for the Pokérus to be randomly🧾 contracted even when another Pokémon
in the party already has it (and the Pokérus can spread after the same battle🧾 where it
was contracted)[3], and there is no location requirement before the Pokérus can
randomly be contracted. Eggs infected with🧾 Pokérus will now indicate as such.
In Ruby
and Sapphire only[4], X values of 0 and 8 do occur naturally, whereas🧾 in Pokémon
Emerald onward, the RNG does not allow them to occur at all. The following is the
chance to🧾 obtain each strain in Ruby and Sapphire:
X values Chance to occur 0
30/255
(11.76470%) 1, 2, 3, 4, 5, 6, 7🧾 31/255
(12.15686%) 8, 9, 10, 11, 12, 13, 14, 15
1/255
(0.39215%)
Generation IV
The mechanics remain the same from Generation III.
Additionally, much🧾 like storage in Pokémon Box Ruby & Sapphire and in the PC, storage
in My Pokémon Ranch will keep a🧾 Pokémon's Pokérus status indefinitely. The Pokérus
doubles the EVs earned from Power items.
In HeartGold and SoulSilver, Professor Elm
calls the🧾 player soon after healing their first Pokémon with the Pokérus to tell them
that it has no effect and will🧾 wear off. If he is called back, he will claim that
Pokémon will level up better with the Pokérus while🧾 infected.
Generation V
The
mechanics remain more or less the same, but now the icon that appears if a Pokémon has
previously🧾 had the Pokérus is pinkish in color instead of the former yellow/orange
color.
Pseudorandom number generation
To determine if any Pokémon in🧾 the player's party
is to be infected, the game calls the Mersenne twister table to get a 32-bit random
number,🧾 discards the lowest 16 bits, and then discards the highest two bits (a bitwise
and with 0x3FFF). If this number🧾 is 0, the game will choose a Pokémon in the party to
be infected.
To determine what party member is to🧾 be infected, the game takes another
value from the Mersenne twister table, multiplies it by the party count, then discards
🧾 the lowest 32 bits of the result. If this number is an Egg, the calculation is
repeated. Otherwise, if that🧾 party member has already been infected, nothing else will
happen.
If a Pokémon will be infected, the game takes the next🧾 value from the Mersenne
twister table and discards the lowest 24 bits (if the lowest three bits of this result
🧾 are all 0, another number is chosen). If any of the highest four bits are nonzero, the
highest five bits🧾 are discarded. The resulting number will be X, the Pokérus strain;
the duration of the virus will be set to🧾 X modulo 4 + 1.
These calculations mean that
the strains 0 and 8 will never occur, and that the remaining🧾 strains are biased towards
the lower numbers (with 1 through 7 being much more common than 9 through 15).
X values
🧾 Chance to occur 0, 8 0/224
(Cannot naturally occur) 1, 2, 3, 4, 5, 6, 7
31/224
(13.83929%) 9, 10, 11, 12,🧾 13, 14, 15 1/224
(0.44643%)
Generation VI
In
Generation VI, the Pokérus does not affect EVs gained from Super Training. However, it
increases🧾 the rate of Double-Up Bags that are received during the training regimen. The
icon that appears if a Pokémon has🧾 the Pokérus has been changed to spell out the full
word, while the cured icon uses a design similar to🧾 the Gen V icon, with the mouth and
eyes having a white color.
Generation VII
During battle, a Pokémon's summary will
display🧾 a "Pokérus" icon beside its name if it has the Pokérus. The icon remains after
the Pokémon is cured. An🧾 Egg infected with the Pokérus does not have this symbol on its
summary screen. It can still spread the virus🧾 normally, and the Pokémon that hatches
from the Egg will immediately acquire the icon.
Pokérus is not present in Pokémon:
Let's🧾 Go, Pikachu! and Let's Go, Eevee!.
Generation VIII
In Sword and Shield, a
Pokémon's summary screen will show the Pokérus icon along🧾 with full text saying
"POKÉRUS" with the typical smile icon next to the text. When cured, this text is then
🧾 removed and only the cured icon is shown. These icons are shown with the rest of the
Pokémon's icons such🧾 as the origin mark and shiny status. In the PC, this text is
removed regardless if the Pokémon is infected🧾 or cured, only showing the face icon
matching the status of infection. It can be seen next to the Pokémon's🧾 type and shiny
status.
In Brilliant Diamond and Shining Pearl, the Pokémon Center nurse will tell the
player that their Pokémon🧾 has been infected with Pokérus like in the original Diamond
and Pearl games. The icon for the games is almost🧾 like how it was in Sword and Shield,
except that the infected icon in the PC preview is contained in🧾 a pink box similar to
how it is presented with text in the summary. The infection text in the Pokémon🧾 summary
is written out as "Pokérus", with a capital P.
Pokérus does not appear natively in
Pokémon Legends: Arceus. It cannot🧾 be contracted naturally, nor can infected Pokémon
spread the virus to other party members. It also cannot progress towards becoming
🧾 cured, and is not displayed on status screens. However, an infected Pokémon transferred
into Legends: Arceus from Pokémon HOME will🧾 still gain bonus EVs during battle, despite
no visible indicators of being infected, cured, or gaining EVs while it remains🧾 in
Legends: Arceus.
Generation IX
In Pokémon Scarlet and Violet, Pokérus no longer
generates naturally, does not spread to adjacent party Pokémon,🧾 cannot be seen on a
Pokémon's summary, and does not provide double effort values during battle. However,
the data itself🧾 is retained in the data structure of the Pokémon, and will remain
stored with the Pokémon if transferred from previous🧾 games via Pokémon HOME into
Scarlet or Violet, despite no longer having any visible indicator nor in-game
effects.
Generation II
"Your Pokémon🧾 appear to have tiny life forms stuck to them.
Your
Pokémon are healthy and seem to be fine.
But we can't tell🧾 you anything more at a
Pokémon Center."
Elm's explanation
"Hello, ?
I discovered an odd
thing.
Apparently there's something called Pokérus that infects Pokémon.
Yes,🧾 it's like
a virus, so it's called Pokérus.
It multiplies fast and infects other Pokémon too. But
that's all.
It doesn't seem🧾 to do anything, and it goes away over time.
I guess it's
nothing to worry about. Bye!"
Generation III
A player being told🧾 their Pokémon has
caught the Pokérus
"Your Pokémon may be infected with Pokérus.
Little is known about
the Pokérus except that they🧾 are microscopic life-forms that attach to Pokémon.
While
infected, Pokémon are said to grow exceptionally well."
Generation IV
"Your Pokémon may
be infected🧾 with the Pokérus.
Little is known about the Pokérus except that they are
microscopic life-forms that attach to Pokémon.
While infected, Pokémon🧾 are said to grow
exceptionally well."
Elm's explanation
When calling the player: "Hello, ?
I
discovered an odd thing.
Apparently there's something called Pokérus🧾 that infects
Pokémon.
Yes, it's like a virus, so it's called Pokérus.
It multiplies fast and infects
other Pokémon too. But that's🧾 all.
It doesn't seem to do anything, and it goes away
over time.
I guess it's nothing to worry about. Bye!"
When called🧾 by the player:
"Hello, ?
It seems that Pokémon that have been infected with Pokérus level up
better.
We're not quite sure🧾 why..."
Generations V-VIII
"Oh... It looks like your
Pokémon may be infected with the Pokérus.
Little is known about the Pokérus, except
that🧾 it is a microscopic life-form that attaches to Pokémon.
While infected, Pokémon
are said to grow exceptionally well."
Status icons
In the anime
In🧾 Oaknapped!, Dr.
Namba explained to Professor Oak that the mysterious viral lifeform Pokérus is an
important component of his Pokémon🧾 Power Acceleration Project (PPAP), a secret project
that aims to infect Pokémon with the Pokérus to evolve them at a🧾 faster rate. However,
all of his specimens had died out. Professor Oak also explains that the term "Pokérus"
was coined🧾 by combining the words "Pokémon" and "virus" together. Later, Professor Oak
began researching about the Pokérus and Team Rocket's true🧾 intentions of using it.
In
the manga
Pokémon Adventures
The Pokérus was discussed in The Final Dimensional Duel
IX, when Platinum's team was🧾 discovered to have this virus and, as a result, became
stronger. Her Froslass, Pachirisu, and Cherrim had it prior to🧾 being taken from the
hospital, and then it spread to the rest of her party. At the hospital, Daisy Oak🧾 and
Yanase Berlitz realize that the infection is, in fact, the Pokérus.
Trivia
The Pokérus
is an example of a mutualistic virus,🧾 in which both host and virus benefit.
In other
languages
Language Title Chinese Cantonese 寶可病毒 Poké Behngduhk Mandarin 寶可病毒 / 宝可病毒
Poké🧾 Bìngdú *
神奇寶貝病毒 Shénqí Bǎobèi Bìngdú * French Pokérus German Pokérus Italian
Pokérus Korean 포켓러스 Pokérus Portuguese Pokérus Spanish Pokérus Vietnamese
🧾 Pokévirus
References
